Adding Serde to syft.js

[cereallarceny]

In this PR we accomplished the following:

1. Got a working example use-case put together with hot reloading.
2. Wrote the entirety of the Serde parser in Javascript. We will need to add further types in the future and there are a few outstanding issues that we're tracking on PySyft: (Everything should simplify as a tuple in serde._simplify PySyft#2422, All strings should simplify without "b" and additional comma PySyft#2423, Serde is potentially simplifying information twice, creating a bad nested structure PySyft#2424)
3. Created a translation layer between Javascript and Python (and back).
4. Created the basic primitives for all types (PointerTensor, TorchTensor, TorchSize, Tuple (imported from another library), Range, Slice, and Plan.
5. We have 100% test coverage across all files (except the index.js, which is currently in flux and going to change dramatically... so I didn't bother).

[codecov]

Codecov Report

Merging #43 into master will increase coverage by 12.3%.
The diff coverage is 98.11%.

@@            Coverage Diff            @@
##           master     #43      +/-   ##
=========================================
+ Coverage      75%   87.3%   +12.3%     
=========================================
  Files           3      12       +9     
  Lines         100     197      +97     
  Branches       16      31      +15     
=========================================
+ Hits           75     172      +97     
  Misses         20      20              
  Partials        5       5

Impacted Files	Coverage Δ
src/index.js	69.51% <0%> (-4.36%)	⬇️
src/custom-types/slice.js	100% <100%> (ø)
src/custom-types/torch-size.js	100% <100%> (ø)
src/custom-types/torch-tensor.js	100% <100%> (ø)
src/custom-types/plan.js	100% <100%> (ø)
src/custom-types/pointer-tensor.js	100% <100%> (ø)
src/_constants.js	100% <100%> (ø)
src/serde.js	100% <100%> (ø)
src/logger.js	100% <100%> (+16.66%)	⬆️
src/custom-types/range.js	100% <100%> (ø)
... and 12 more

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[iamtrask]

Absolutely fantastic work! Impressively fast turnaround as well!